The present invention relates to a pipe joint capable of enhancing a working property when a tapered male screw section of a pin is perpendicularly inserted into a tapered female screw section of a box or coupling and successively turned so that the male screw section can be screwed into the female screw section.
Conventionally, as a pipe joint used for an oil well pipe, a pipe pile for construction work and so forth, there is provided a joint composed of a tapered square thread for pipe use including a trapezoidal screw thread and buttress screw thread in which a tapered male screw section 52 of a pin 51 of a pipe 50 is engaged with a tapered female screw section 55 of a box 54 of a short pipe 53 as shown in FIGS. 9(A) and 9(B). FIG. 9(B) is an enlarged view showing a state of starting the engagement of this tapered square screw joint for pipe use.
In order to clearly explain the stabbing property (a performance of the connection can be made up immediately after stabbing) of the tapered square screw joint, a profile of a male thread ridge 56 of the tapered male screw section 52 is made to be the same as that of a female thread ridge 57 of the tapered female screw section 55, and a top face 58 of the ridge of the male screw and a top face 59 of the ridge of the female screw are made to be parallel to tapered face Tf. FIG. 9(B) is a cross-sectional view showing a state of engagement of the ridge of the male screw 56 with the ridge of the female screw 57 which are going to engage with each other. That is, a tapered face, on which top faces 58 of the ridges of the male screw- section 52 are continuously arranged, and a tapered face, on which top faces 59 of the ridges of the female screw section 55 are continuously arranged, precisely coincide with each other. In this drawing, a position of the tapered male screw section 52 in the circumferential direction is set at a position of the tapered female screw section 55 in the circumferential direction so that the ridges 56 of the male screw section can be located at bottoms 60 of the ridges 57 of the female screw section. As can be clearly seen in the drawing, it is impossible to screw the tapered male screw section 52 into the tapered female screw section 55 in the above state.
Referring to FIG. 10(B) showing a buttress screw joint of API, which is commonly used as an oil well pipe screw, the stabbing property of a square screw joint for pipe use will be explained below. In this case, explanations will be made into a mechanism in which a male thread ridge 63 and a female thread ridge 64 are screwed into bottoms of the threads after the tapered male screw section 61 has been inserted into the tapered female screw section 62.
Elements of the buttress screw of API are described as follows. Taper T={fraction (1/16)} (or 62.5 mm/m). This taper is a ratio of change in the diameter. Pitch P=5.08 mm. Height of the ridge H=1.575 mm. Stabbing flank angle xcex7=10xc2x0. Load flank angle xcex3=3xc2x0. Straight line sections of the top faces 65, 66 of the ridges of the male and the female screw are parallel to tapered face Tp (pitch line). Corner R of the top face 65 of the male screw is 0.76 mm and corner R of the top face 66 of the female screw is 0.2 mm.
FIG. 10(A) is a view showing a state in which the tapered male screw section 61 is fitted into the tapered female screw section 62 in the most appropriate circumferential direction. Different from the above case into which the tapered square screw joint for pipe use is incorporated, an opening section 68 of a bottom 67 of the tapered female screw section 62 is larger than the top face 65 of the ridge 63 of the male screw, and when R is formed at the corner, the difference can be further increased. When the tapered male screw section 61 is perpendicularly dropped in the above condition, a corner section 69 of the male ridge 63 of the tapered male screw section 61 can be slightly mounted on a corner section 70 of the ridge 64 of the tapered female screw section 62. When the tapered male screw section 61 is turned in the above state, the tapered males crew section 61 is spirally fitted into the tapered female screw section 62.
In order to fit the tapered male screw section 61 into the tapered female screw section 62, relative positions of the male and the female screw line are not necessarily limited to the positions shown in FIG. 10(A). The tapered male screw section 61 can be fitted into the tapered female screw section 62 even at apposition at which the tapered female screw section 61 is shifted downward from the position shown in FIG. 10(A) so that corner R of the stabbing flank face 71 of the ridge 63 of the male screw section comes into contact with corner R of the stabbing flank face 72 of the tapered female screw section 62. When the tapered male screw section 61 is screwed into the tapered female screw section 62 by an angle in the circumferential direction corresponding to this shift, an allowance can be provided in the circumferential direction so that the tapered male screw section 61 can be properly screwed into the tapered female screw section 62.
In normal inserting and screwing work, the tapered male screw section 61 is inserted into the tapered female screw section 62, and then the tapered male screw section 61 is turned to the above circumferential position at which the ridge 63 of the tapered male screw section 61 can be properly mounted on the ridge 64 of the tapered female screw section 62. Since the ridge 63 of the male screw section has not been engaged yet with the ridge 64 of the female screw section at this time, there is a possibility that gall occurs unless the axis of the tapered male screw section 61 agrees with the axis of the tapered female screw section 62. In the case of a conductor casing, the diameter of which is large, since the rotational angle is large, it is difficult to search for the screwing position. Accordingly, when a range is large, in which the circumferential position at which the ridge 63 of the male screw section is screwed to the ridge 64 of the female screw section, it possible to reduce a rotational angle necessary for turning the male screw section to an appropriate position, that is, the stabbing property of the tapered screw joint is high. When clearance G between width W of the opening section 68 of the bottom 67 of the tapered female screw section 62 and width V of the top face 65 of the ridge of the tapered male section is large, another advantage can be provided as follows. When the tapered male screw section 61 is dropped by an amount corresponding to clearance G so that the tapered male screw section 61 is mounted on the stabbing flank face 72 of the ridge 64 of the tapered female screw section 62, it is possible to ensure a distance (clearance G in the axial direction of the pipe xc3x97taper T)/2 for mounting the tapered male screw section 61 on the stabbing flank face 72 of the ridge 64 of the tapered female screw section 62 in the radial direction. Therefore, it is possible to screw the tapered male screw section into the tapered female screw section stably.
As can be understood by the above explanations, the stabbing property, which is defined as a performance by which the tapered male screw section can be smoothly screwed into the tapered female screw section after the tapered male screw section has been inserted into the tapered female screw section, is enhanced when a circumferential range (xcex8) in which screwing can be started at a position as it is when the tapered male screw section 61 is inserted into the tapered female screw section 62, and also the stabbing property is enhanced when a depth xcex4, by which the stabbing flank face 71 of the male thread ridge 63 is mounted on the stabbing flank face 72 of the female thread ridge 64, is large, wherein the depth xcex4 is the same as the distance in which the tapered male screw section 61 is mounted on the stabbing flank face 72 of the female ridge 64. Angle xcex8 and depth xcex4, which control the stabbing property, will be explained referring to some examples of the conventional tapered screw joint.
First, a buttress joint of API will be explained below. As shown in FIG. 10(B), first, an angle of the stabbing flank 71 of the ridge 63 of the tapered male screw section 61, that is, a stabbing flank angle xcex7 is inclined by the angle of 10xc2x0 with respect to a face perpendicular to pipe axis C. The larger the inclination of the stabbing flank angle xcex7 is, the larger the clearance G of engagement becomes. Secondly, R=0.76 mm is provided in the corner 69 of the stabbing flank face 71 of the ridge 63 of the tapered male screw section 61, and clearance G is further extended. Furthermore, when the tapered male screw section 61 is a little more slender than the tapered female screw section 62, that is, when the tapered male screw section 61 is more slender than that of the tapered female screw section 62 by 0.03 mm in a direction of the screw axis, and when R is provided in the corners 75, 76 formed by the top faces 65, 66 of the ridges of the male and the female screw sections and the load flank faces 73, 74, the clearance G can be further extended. In FIG. 10(B), R=0.20 mm. Due to the foregoing, clearance G is a little extended. In this case, a total of all clearances is approximately estimated to be 1.75 mm. When this value is converted into a range (xcex8) in the circumferential direction, xcex8=(360xc2x0xc3x971.75)/5.08=124xc2x0. On the other hand, depth (xcex4) is determined by xcex4=1.75/32=0.055 mm.
Next, a Seal-Lock Joint manufactured by Aramco Co. will be explained below. In this special joint, first, the stabbing flank angle xcex7 on the insertion side is inclined by 45xc2x0 with respect to a face perpendicular to the pipe axis. Secondly, top faces of the male and the female screw section are made to be parallel to the pipe axis. Therefore, when the tapered male screw section is inserted into the tapered female screw section, it is difficult for the male ridge and the female ridge to be stuck with each other.
Further, in a special joint manufactured by Vetco-Gray Co., when a fourfold-start screw thread is applied, there are provided four screwing positions in one round of 360xc2x0. Therefore, after the tapered male screw section has been inserted into the tapered female screw section, screwing can be accomplished by turning the screw section only a little. In this connection, in the case of a normal single-start screw thread, the number of screwing sections is one.
The most remarkable characteristic of a multiples-start screw threads, the number of threads of which is xe2x80x9cnxe2x80x9d, is that the number of rotations necessary for screwing is 1/n compared with the single-start screw thread. This is a very important factor in the case of a joint of large diameter which is tightened by a rope and the like.
There is provided another special joint in which an entrance of the tapered female screw section is formed long, that is, a stabbing guide is arranged at the entrance, so that the tapered male screw section can be straight inserted into the tapered female screw section.
However, the above conventional pipe joints have the following problems to be solved.
In the case of a single-start screw thread, the inserting position does not necessarily agree with the starting position of screwing. Therefore, in order to search the screwing position, it is necessary to turn the tapered female screw section.
On the other hand, in the case of a multiple-start screw thread including a fourfold-start screw thread, there are provided a plurality of screwing positions, the number of which is the same as the number of threads. Therefore, the number of turns can be reduced in the process of adjustment. Due to the foregoing, the stabbing property can be considerably improved compared with a single-start screw thread. Even when the stabbing property is considerably improved, it is impossible to immediately start inserting the tapered male screw section into the tapered female screw section.
In the case of a pipe joint having a stabbing guide, it is possible to prevent the occurrence of problems such as gall which is caused when the screw is obliquely inserted, however, it is impossible to start screwing immediately after the insertion.
The present invention has been achieved in view of the above circumstances. It is an object of the present invention to provide a pipe joint capable of being screwed quickly and easily from a position at which a tapered male screw section having a single or multiple-start screw thread is inserted into a tapered female screw section.
The first invention of the present invention to accomplish the above object provides a pipe joint comprising: a pin having a tapered male screw section formed on an outer circumferential face of an end of a pipe; a box having a tapered female screw section, which can be screwed to the tapered male screw section, formed on an inner circumferential face of an end of a pipe, wherein the tapered male screw section is screwed into the tapered female screw section, a top face of a male thread ridge of the tapered male screw section and a top face of a female thread ridge of the tapered female screw section have a predetermined width like a square screw thread, trapezoidal screw thread and buttress screw thread, and top faces of both thread ridges are inclined in a direction opposite to a tapered face of screw threads with respect to a face parallel to the pipe axis.
The second invention provides a pipe joint comprising: a pin having a tapered male screw section formed on an outer circumferential face of an end of a pipe; a coupling having tapered female screw sections, which can be screwed to the tapered male screw section, formed on inner circumferential faces of both ends of a short pipe, wherein the tapered male screw section is screwed into the tapered female screw section, a top face of a male thread ridge of the tapered male screw section and a top face of a female thread ridge of the tapered female screw section have a predetermined width like a square screw thread, trapezoidal screw thread and buttress screw thread, and top faces of both thread ridges are inclined in a direction opposite to a tapered face of screw threads with respect to a face parallel to the pipe axis.
The third invention provides a pipe joint comprising: a pin having a tapered male screw section formed on an outer circumferential face of an end of a pipe; a box having a tapered female screw section, which can be screwed to the tapered male screw section, formed on an inner circumferential face of an end of a pipe, wherein the tapered male screw section is screwed into the tapered female screw section, a top face of a male thread ridge of the tapered male screw section and a top face of a female thread ridge of the tapered female screw section have a predetermined width like a square screw thread, trapezoidal screw thread and buttress screw thread, portions of top faces of both thread ridges are inclined in a direction opposite to a tapered face of a screw thread with respect to a face parallel to the pipe axis, and the rest of top faces of both thread ridges are made parallel to the pipe axis.
The fourth invention provides a pipe joint comprising: a pin having a tapered male screw section formed on an outer circumferential face of an end of a pipe; a coupling having tapered female screw sections, which can be screwed to the tapered male screw section, formed on inner circumferential faces of both ends of a short pipe, wherein the tapered male screw section is screwed into the tapered female screw section, a top face of a male thread ridge of the tapered male screw section and a top face of a female thread ridge of the tapered female screw section have a predetermined width like a square screw thread, trapezoidal screw thread and buttress screw thread, portions of top faces of both thread ridges are inclined in a direction opposite to a tapered face of screw threads with respect to a face parallel to the pipe axis, and the rest of top faces of both thread ridges are made parallel to the pipe axis.
The fifth invention provides a pipe joint comprising: a pin having a tapered male screw section formed on an outer circumferential face of an end of a pipe; a box having a tapered female screw section, which can be screwed to the tapered male screw section, formed on an inner circumferential face of an end of a pipe, wherein a multiple-start screw thread is applied, in the case of an odd screw thread, a row of threads is composed of high male and female thread ridges, which are arranged every thread ridges, the number of which is (number of thread ridgesxe2x80x941), and also composed of low male and female thread ridges arranged between the high male and female thread ridges, in the case of an even screw thread, a row of screw threads is composed of high male and female thread ridges and low male and female thread ridges which are alternately arranged, or a row of threads is composed of high male and female thread ridges, which are arranged every thread ridges, the number of which is (number of thread ridgesxe2x80x941), and also composed of low male and female thread ridges arranged between the high male and female thread ridges.
The sixth invention provides a pipe joint comprising: a pin having a tapered male screw section formed on an outer circumferential face of an end of a pipe; a coupling having tapered female screw sections, which can be screwed to the tapered male screw section, formed on inner circumferential faces of both ends of a short pipe, wherein a multiple-start screw thread is applied, in the case of an odd screw thread, a row of threads is composed of high male and female thread ridges, which are arranged every thread ridges, the number of which is (number of thread ridgesxe2x80x941), and also composed of low male and female thread ridges arranged between the high male and female thread ridges,
in the case of an even screw thread, a row of screw threads is composed of high male and female thread ridges and low male and female thread ridges which are alternately arranged, or a row of threads is composed of high male and female thread ridges, which are arranged every thread ridges, the number of which is (number of thread ridgesxe2x80x941), and also composed of low male and female thread ridges arranged between the high male and female thread ridges.
The seventh invention provides a pipe joint wherein a top face of a male thread ridge of the male screw section and a top face of a female thread ridge of the female screw section have a predetermined width like a square screw thread, trapezoidal screw thread and buttress screw thread, and top faces of both thread ridges are inclined in a direction opposite to a tapered face of screw thread with respect to a face parallel to the pipe axis.
The eighth invention provides a pipe joint wherein a top face of a male thread ridge of the male screw section and a top face of a female thread ridge of the female screw section have a predetermined width like a square screw thread, trapezoidal screw thread and buttress""screw thread, and top faces of both thread ridges are inclined in a direction opposite to a tapered face of screw threads with respect to a face parallel to the pipe axis.
The ninth invention provides a pipe joint comprising: a pin having a tapered male screw section formed on an outer circumferential face of an end of a pipe; a box having a tapered female screw section, which can be screwed to the tapered male screw section, formed on an inner circumferential face of an end of a pipe, wherein marks to make the tapered male screw section agree with the tapered female screw section in the circumferential direction are attached in the process of thread cutting so that an original positional relation between the male thread row and the female thread row can be reproduced in which the stabbing flank face of the male thread ridge is set on the stabbing flank face of the female thread ridge without the occurrence of sticking between the top face of the thread ridge of the male screw section and the top face of the thread ridge of the female screw section when the tapered male screw section is lowered in a perpendicular direction under the condition that a virtual tapered face coming into contact with the top face of the thread ridge of the tapered male screw section and a virtual tapered face coming into contact with the top face of the thread ridge of the tapered female screw section, agree with each other when the tapered male screw section is inserted into the tapered female screw section.
The tenth invention provides a pipe joint comprising: a pin having a tapered male screw section formed on an outer circumferential face of an end of a pipe; a coupling having tapered female screw sections, which can be screwed to the tapered male screw section, formed on inner circumferential faces of both ends of a short pipe, wherein marks to make the tapered male screw section agree with the tapered female screw section in the circumferential direction are attached in the process of thread cutting so that an original positional relation between the male thread row and the female thread row can be reproduced in which the stabbing flank face of the male thread ridge is set on the stabbing flank face of the female thread ridge without the occurrence of competition between the top face of the thread ridge of the male screw section and the top face of the thread ridge of the female screw section when the tapered male screw section is lowered in a perpendicular direction under the condition that a virtual tapered face coming into contact with the top face of the thread ridge of the tapered male screw section and a virtual tapered face coming into contact with the top face of the thread ridge of the tapered female screw section, agree with each other when the tapered male screw section is inserted into the tapered female screw section.